Prepreg tape slitting method and apparatus

ABSTRACT

Improved methods and apparatus are provided for the production of prepreg slit tape wherein master rolls of prepreg sheet are formed which are capable of being slit, with liner attached, at high precision.

RELATED APPLICATION

The present application is a continuation application of allowed U.S.patent application Ser. No. 13/627,067, filed Sep. 26, 2012.

FIELD OF THE INVENTION

The present application is directed to a method of and apparatus forpreparing improved master rolls of prepreg sheet materials for slitting,the improved master rolls so formed, and a simplified slitting apparatusfor slitting the improved master rolls. Specifically, the presentapplication is directed to a method of and apparatus for preparingimproved master rolls of prepreg sheet material wherein the improvementlies in the application of a liner material which is suitable for andremains affixed to the prepreg material during slitting withoutcompromising the slitting process or the slit tape formed. In following,the present application is also directed to an improved method ofgreatly simplified apparatus for slitting prepreg sheet materials whichmethod allows for the slitting of the prepreg sheet material withouthaving to remove the backing before passing the prepreg materialsthrough the slitter.

BACKGROUND

Advances in composite technology have had a marked impact on productdesign and engineering and, ultimately, manufacture. Early methodsinvolving hand lay-up of fibrous materials and sheets with thesubsequent impregnation of the laid up materials and, subsequently, thelaying up of pre-impregnated fibrous sheets and mats followed bycompression forming and curing saw rapid adoption and exploitation ofthese composite materials and technologies in many fields. However,while useful for many applications, the slow methodical build-up of thelayers of materials is very labor intensive, oftentimes involves the useof hazardous chemicals and, more importantly, employs unstable materialsand/or materials having limited working time. Thus, while a markedadvance in the industry, their applications were still limited andcostly.

Subsequent advances in composite materials and technology led tocontinuous manufacturing techniques. Perhaps the most notable of thesetechniques is filament winding wherein a continuous tow of certainfibrous materials were pulled though a bath of a curable material toimpregnate the same with the curable material, the wet tow is then woundabout a mandrel to form the desired part, preferably with some measureof immediate cure (oftentimes a UV cure) to attain a green state so asto prevent excessive flow of the resin material and maintain the fiberplacement during the winding process following which the wound structureis fully cured. However, these operations are very slow and timeconsuming owing, in large part, to the narrow width of the tow. Moreimportantly, these processes are very capital intensive as the whole ofthe operation, from preparation of the curable composition to thewetting of the tow of fiber material and, subsequently, to the formationof the part itself, all had to be performed in the same immediatevicinity of one another, typically on the same floor space.

Continued advances in both manufacturing and materials technology led tothe ability to prepare cut sheets and, subsequently, master rolls of“green state” or partially cured prepreg materials: the latter in theform of continuous strips and sheets of tows of woven fibers orunidirectional, parallel fibers, most typically glass or carbon fibers,impregnated with a thermoset/thermosetting resin, especially epoxy, BMIor Polyimide resins. These prepreg materials are generally formed on asupport sheet material, typically paper, which also serves as aseparator or liner material to prevent successive layers, in the case ofstacked cut sheets, or successive windings, in the case of master rolls,of the prepreg materials from contacting and adhering or melding to oneanother. The so formed cut sheets and master rolls of prepreg materialsare then stored and shipped to the ultimate end-user for use inmanufacturing composite structures. Owing to the unstable nature of thethermoset/thermosetting resin material, these cut sheets and masterrolls are stored and maintained at significantly reduced temperatures,oftentimes at or below freezing, until use or further processing so asto prevent or at least significantly retard premature curing of thethermoset resin. The inherent cost advantages and focus on centeredexpertise (e.g., prepreg manufacturers concentrated on the chemistry andmanufacture of the prepreg materials and the product manufacturersconcentrated on the layup process) proved beneficial all around. Nolonger was it necessary for the ultimate composite product manufacturerto invest in the capital equipment, consumable materials, overhead,spatial requirements, and technical expertise and personnel to make theprepreg materials.

Advances have also been made whereby the prepreg materials may be formedusing a thermoplastic resin, rather than a thermoset/thermosettingresin. Here the thermoplastic polymer is heated to a soften, flowable orat least readily pliable state and combined with and infiltrated throughthe fibers. This may be accomplished by many known methods includingextrusion/co-extrusion, pultrusion, vacuum/pressure molding, injectionmolding, etc., to form the prepreg materials, also known as compositematerials. These prepreg materials are mated with a liner as they arebeing formed or subsequent thereto but prior to stacking or rolling.

Early on, master rolls of prepreg strip or sheet materials weremanufactured in standard widths that were then used to make thecommercial products. This was acceptable as many applications had verysimilar demands and requirements, e.g., baseball bats, golf clubs,hockey sticks, lacrosse sticks and the like can all be made withgenerally the same width of slit tape, largely because the demands aresimilar and the need for differentiation less. Even if not optimal,these stock rolls were used nonetheless as making many different widths,especially making custom widths, was cost prohibitive: the capitalrequirements are quite large and incapable of supporting a largedifferentiation of product widths. Consequently, the full adoption ofthis technology in higher demanding and higher tech applications waslimited if the width of the tapes needed were inconsistent with thewidths that were available.

More recently, the technology has evolved and new expertise andprocessing capabilities have been developed whereby a broad array oftape widths are made possible through the slitting of stock masterrolls. Specifically, slitting apparatus and equipment has been developedwhich allows one to unwind the master rolls of prepreg material, removethe liner, pass the prepreg material through a slitter whose cuttingelements, e.g., knives or blades, are spaced to produce the desiredwidths of tape, and rewind the so formed prepreg slit tape, commonlyreferred to as just “slit tape,” with a new liner, preferably a polymerliner. This innovation allowed for the production of wide slit tape foruse in the manufacture of large planar or curved planar surfaces as wellas narrow width slit tape for use in the manufacture of more intricateparts and/or parts having multiple changes in surface orientation.

Although the advent of slit tape allowed for the use of prepregmaterials in the manufacture of many different products whose demands,especially physical demands, required specific properties which areaffected by, in part, the width of the prepreg slit tape, limitationsstill existed. Specifically, the extension of the use of slit tape intohigh tech applications, especially in the production of components foraerospace and aircraft production, has placed increased demands onconsistency and tight tolerances in the slit tape, both in terms of themake-up and dimensions of the slit tapes. While one might think that thedemands for aerospace and aircraft production would be fairly constant,nothing could be further from reality. Each component for aerospace andaircraft production must endure a combination of environment conditionsand physical demands and stresses that are most often unique to thatcomponent. For example the requirements of the tail fin of an aircraftwill be markedly different from those of a wing or a fuselage portion.Similarly, the shapes of such components vary from generally smooth,curved structures, as with a fuselage, to multi-oriented surfaces withsharp angles, as with a tail fin.

In order to meet the requirements for aircraft and aerospaceapplications, it has become more and more apparent that a plethora ofwidths of slit tape are needed with differences in the width of the slittape from one application to the another oftentimes being on the orderof just fractions of an inch. Furthermore, and perhaps more importantly,these applications demand extremely tight tolerances in relation to anyvariation in the width of the slit tape for a given application, withtolerances being orders of magnitude smaller than for most commercialapplications. In aerospace, it is not uncommon for tolerances in widthto be on the order of thousandths, if not ten-thousandths, of an inch.

However, the requirements do not end there as slit tape for these andother high tech applications must also be free of artifacts, whether offoreign origin or which original from the master prepreg materialsthemselves. The former can be controlled by proper environmentalcontrols and clean-room type practices. The latter, however, requirescare in the selection and implementation of materials, apparatus andmethods or processes. For example, poor quality cutting elements, e.g.,knives or blades, and/or improper or too infrequent cleaning thereof maylead to a buildup of resin on the blade which, in turn, may attach to orfall on the slit tape as it moves out of the slitter. While suchartifacts are generally not problematic in the winding of the slit tape,the concern here is that such artifacts may create or lead to apotential failure point in the part to the made.

As noted above, slit tape is typically formed by unwinding the masterroll of prepreg material, removing the backing (which also acts as aliner for the master roll), passing the prepreg material through aslitter whose cutting elements, e.g., knives are spaced to produce thedesired widths of slit tape, and rewinding the so formed slit tape witha new liner. Removing the backing from the master roll prior to theslitting operation is critical in order to meet the tight tolerances andartifact free requirement for high tech applications, especiallyaerospace and aircraft production.

The most common backing material used in the production of master rollsis paper. Because paper is comprised of fibrous materials whoseorientation is random, it is difficult, if not impossible, to avoid theformation or accumulation of fibrils along the cut edge of the paper aswell as the generation of free fibrils and paper dust which becomeairborne. These loose fibrils and the paper dust then adhere to andcomprise undesired artifacts on the slit tape itself. The degree towhich such fibrils and paper dust form is, in part, dependent upon thequality and condition of the slitting knives or blades themselves, withmore being formed as the knives or blades become worn. Of course, it isto be appreciated that the coarse nature of the paper would also hastenthe wearing of the knife of blade.

In addition to an increase in the generation of fibrils and paper dust,poor quality and/or worn knives and blades leads to or increases therate of the buildup of fibrils and/or resin on the blade, which affectsthe consistency of the cut as well as, again, the deposit of artifactson the slit tape. Furthermore, when paper is moving across a stationaryknife or blade, especially one that is worn, there is the tendency forthe paper to catch on the knife or blade. This happenstance may lead toa tear in the paper and/or, more critically, an unexpected jolt, snag,or stall in the slitting process, which, in turn, causes a movement inthe prepreg and slit tape as it is being formed and, hence, a variationin the width of the slit tape and/or a tear or break in the slit tapeitself.

Although paper as the backing still dominates, one or two manufacturershave recently experimented with and produced prepregs using a polymerbacking, a polymer film or fabric, owing to their cost-effectiveness.However, like paper, there are no set requirements as to the integrity,nature, orientation, or physical properties of these polymer backings ortheir peel strength relative to the prepreg material as their solepurpose is merely to serve as the foundation in the manufacture of theprepreg material and, subsequently, the separator between successivewindings thereof in forming the master rolls. However, while costeffective, polymer backings have some similar problems as well as uniqueproblems associated with their use. For example, unlike paper, whichlies flat and has a consistent tautness across its surface, polymerbackings, owing to their more supple nature, tend not to lie flat andmay and/or fail to lie with a consistent stress or tautness across theirsurface. Furthermore, unlike paper whose porosity allows for the escapeof air trapped between the prepreg material and the paper, polymer filmsprovide no path of escape and, consequently, air pockets form that arethen wound into the subsequently formed master rolls.

Each of the foregoing factors affects the integrity of the interfacebetween the prepreg material and the polymer backing. For example, foldsin or bunching up of the polymer backing and/or the presence of airpockets trapped between the prepreg material and the backing createareas where there is no direct contact or adherence between the prepregand the backing. In master rolls, this is not an issue, but in formingslit tape it would be devastating. Specifically, were one to try to slitthese materials without removing the backing, the lack of adherencebetween the backing and prepreg material allows for relative motion ormovement of one to the other during the slitting process which adverselyaffects the final dimensions of the slit material. Depending upon theextent of the bunching of the polymer backing and/or the size of thearea lacking contact, this could also lead to a jam in the slitter,necessitating one to shut down the process to rectify the situation. Ajam also raises the risk for compromising the slit tape structurally anddimensionally, including those slit tape tows that would otherwise havebeen in specification. Furthermore, assuming that the problem areapassed through the slitter without problem, without a bond between theprepreg material and the backing, there is the likelihood, if notcertainty, of misalignment between the two as the slit tape is beingwound. Consequently, the opportunity exists for prepreg on prepreg insuch windings whereby the successive layers in contact with each otherbond or meld together making the roll unsuitable for subsequentmanufacturing applications. Hence, it is critical to remove the polymerbacking to slitting as well.

Equally critical to the typical prepreg slitting operation is the needto insert a new liner, a polymer liner or, more commonly, a polyliner,as the slit tape is being wound so as to prevent bonding or melding ofone layer of slit tape to another. This interlining or interleafingprocess, as it is commonly referred, requires great precision both interms of alignment and tension of the liner and slit tape as one mustdirectly align the narrow strip of slit tape with the liner as well asensure good mating between the two so that the two do not move relativeto one another in the final winding step. In part, this is addressed byemploying a liner material that is somewhat wider than the slit tape.However, even that has its limitations as one can only economically andfunctionally use a liner whose width is marginally wider than the slittape, perhaps 10 to 20 percent, in the case of narrow tapes, somewhatless in the case of wide tapes. Though the additional width is quitesmall, over the miles and miles of slit tape produced the addedmaterials costs begin to add up.

Additionally, the use of wider liner material affects the consistency orevenness of the winding, particularly in helical windings, as ridges andvalleys form reflecting those areas of the winding where slit tape isand is not present. Similarly, in spool windings, it is difficult todirectly align the slit tape over itself as the outer edges of the linerorient the winding as it occurs. Lastly, since most specifications forslit tape are weight and/or size limited, the excess liner affects theamount of prepreg slit tape that can be wound on any given spool orspindle.

The second key factor in addressing alignment concerns and the integrityof the contact between the slit tape and liner is the liner feed andalignment system itself. Owing to the speed of these systems as well asthe narrow widths of slit tape being produced, liner feed and alignmentsystems require a large degree of sophistication in order to properlyalign the liner with the slit tape and to do so under a constant tensionto ensure good liner to slit tape contact across the whole of the widthof the slit tape. Yet, suitable liner feed and alignment systems entailsignificant capital expense: an expense that is only multiplied as eachwinding station must have its own liner feed and alignment capability.Thus, if one has 64 winding heads, one needs 64 liner feed andassociated alignment systems.

Thus, despite all the advances that have been made, there still remainsa need in the industry for a simpler, less capital intensive and lesscostly process and apparatus for producing of slit tapes.

More importantly, there still remains a need in the industry for such aprocess and apparatus that can be implemented without a significantcapital investment and without compromising or sacrificing productionrate and quality.

SUMMARY

According to the present teachings there is provided a simplified, lesscapital intensive, and less costly method for the production of slittape which method does not require the removal of the backing materialfrom the master roll of prepreg sheet material as it is being fed intothe slitter. Specifically, there is provided a method for the productionof slit tape which method involves unwinding the master roll of prepregsheet material with liner attached, passing the same through theslitter, thereby simultaneously slitting the prepreg sheet and liner,and winding the so formed slit tape, with liner attached. This processis further characterized as employing a master roll of prepreg sheetwhose liner is a polymer film having certain predefined physicalproperties and attributes which a) enable its slitting without tearing,without the formation of fibrils, and without separating from theprepreg material; b) enables its winding without elongation or thecreation of stress fractures in the film; and c) manifests a constant orsubstantially constant peel strength with the prepreg material.

According to a second aspect of the present teaching there is provided asimplified and less capital intensive apparatus for the conversion ofprepreg master roll to slit tape which apparatus is either free ofmaster roll backing removal and winding apparatus or has, in additionthereto, a polymer film liner supply and alignment apparatus forreplacing the backing with a polymer film liner. The apparatus is alsofree of liner feed and alignment apparatus associated with its slit tapewinding heads.

According to a third aspect of the present teachings there is provided amethod for the production of master rolls suitable for use in theabove-referenced method which method involves replacing the liner orbacking material used in the formation of the prepreg sheet materialwith a polymer film having certain predefined physical properties andattributes which a) enable its slitting without tearing, without theformation of fibrils, and without separating from the prepreg material;b) enables its winding without elongation or the creation of stressfractures in the film; and c) manifests a constant or substantiallyconstant peel strength with the prepreg material. The replacement may beperformed in-line during the preparation of the prepreg sheet materialprior to winding on the master roll or it may performed after winding ofthe master roll but prior to slitting. In the former, the replacement isperformed by the prepreg manufacturer whereas the latter may beperformed by the prepreg manufacturer or anyone else prior to slitting.

According to a fourth aspect of the present teaching there is providedan apparatus for the in-line replacement of the liner or backingmaterial used in the formation of the prepreg sheet with theaforementioned polymer film prior to winding of the master roll.

According to a fifth aspect of the present teaching there is provided anapparatus for the conversion of conventional master rolls to masterrolls wherein the backing is removed and replaced with a polymer filmliner before the prepreg is rewound into an improved master roll.

According to a sixth aspect of the present teaching there is provided aprepreg slitting apparatus wherein the backing is removed as the prepregis unwound from the master roll and replaced with a polymer film linerbefore the prepreg is advanced to the slitter.

Finally, according to a seventh aspect of the teaching of the presentapplication there is provided novel master rolls of prepreg sheetmaterial which are characterized as being capable of being slit with theliner attached while maintaining product integrity and tolerances.Specifically, there are provided master rolls wherein successivewindings of the prepreg sheet material are separated by a polymer filmwhich, when slit in combination with the prepreg material, is capable ofbeing slit without tearing, without the formation of fibrils, andwithout separating from the prepreg material; which allows for itswinding without elongation or the creation of stress fractures in thefilm; and which manifests a constant or substantially constant peelstrength with the prepreg material.

These and other aspects, details and benefits of the present teachingswill be more fully described in and apparent from the specificationbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings which form a part of the specification are tobe read in conjunction therewith. Like reference numerals are employedto indicate like parts in the various views.

FIG. 1 is a schematic side view of a conventional, slitting and windingapparatus.

FIG. 2 is a schematic side view of a simplified slitting and windingapparatus used in the practice of the present teachings.

FIGS. 3A, 3B and 3C are schematic side views of a portion of a prepregsheet manufacturing apparatus incorporating, at various points, thecapability for the in-line replacement of the backing with a polymerfilm liner according to the present teachings.

FIG. 4 is a schematic side view of a converting apparatus for convertinga conventional master roll into the improved master rolls suitable foruse in the practice of the present teaching.

DETAILED DESCRIPTION

As used herein and in the appended claims, the term “continuous” whenused in reference to the prepreg sheet material and slit tape refers tolong lengths of such materials whereby these materials are wound forstorage and/or transportation. Typically, continuous prepreg sheets andtapes will have lengths of from at least about 10 meters, more typically25 meters, up to about 1000 meters or more and widths of from about 0.1meters to 2.5 meters, preferably from about 0.7 meters to about 1.5meters. Additionally, although specific reference herein is made toprepreg sheet materials of unidirectional carbon fibers impregnated withcurable epoxy resins, it is understood that the present teachings arenot so limited. Indeed, the present teachings are equally applicable toother prepreg sheet materials, including those made of glass fibers,polymer fibers, and combinations of fibers, as well as those wherein thematrix resin is any of number of curable or thermosetting matrix resinsincluding, but not limited to epoxies, cyanate esters, bismaleimides,phenolics, polyimides, and the like or a thermoplastic resin such aspolyethylene, polypropylene, polyamide, polyphenylene sulfide,polyetherimide, polyetheretherketone, polyetherketoneketone, and thelike, or combinations of thermoset resins, thermoplastic resins or both.

While few details are provided herein with respect to the elements ofthe apparatus as well as the apparatus as a whole, other than therevisions made herein, such details and information are well known tothose skilled in the art and available commercially: thus, a lengthydetailed disclosure is not necessary. For example, suitable slitterstypically comprise one or more cutting elements in combination withrollers and/or alignment means wherein the cutting elements are of thetype known to be suitable for the cutting of prepreg materials for hightech applications. Similarly, little if anything is said in relation tothe elements and components of the apparatus responsible for advancingthe materials from one roll to another or for winding or unwinding thematerials. In this regard, it is to be appreciated that the apparatus asdescribed herein includes a plurality of motor driven axels or hubs uponwhich the various rolls, spindles, spools, etc., mentioned herein aremounted, thereby aiding the unwinding and winding of the variousmaterials. In addition to the foregoing, the system may integratemotorized pinch rollers for further assisting in the draw and/oradvancing of the various tape materials. Those, skilled in the art,having the benefit of the present disclosure and appended drawings willreadily appreciate the placement and types of motor driven axels andhubs necessary.

According to the present teachings there is provided:

-   -   a method for the production slit tape which method does not        require the removal of the backing or liner material from the        master roll of prepreg sheet material as it is being fed into        the slitter for forming the slit tape or the interleafing of a        liner material as the slit tape is being wound;    -   a method for the production slit tape which method includes the        removal of the backing material and replacement thereof with a        polymer film liner prior to slitting and eliminates the need to        interleaf a new liner material as the slit tape is being wound    -   apparatus for performing the aforementioned slitting processes;    -   a method for the production of master rolls of prepreg sheet        materials for use in the aforementioned slitting process;    -   an apparatus for producing the aforementioned master rolls        in-line during the production of the prepreg sheet materials;    -   a method of converting conventional master rolls of prepreg        sheet material to master rolls suitable for use in the        aforementioned slitting process;    -   an apparatus for converting conventional master rolls to master        rolls suitable for use in the aforementioned slitting process;        and    -   master rolls of prepreg sheet material suitable for use in the        aforementioned slitting process.

Each of these teachings is premised upon the production and use ofmaster rolls of prepreg sheet material which are characterized as beingcapable of being slit with the liner attached without adverselyaffecting product integrity, production tolerances, and processefficiency: indeed, if anything, the these attributes and others areimproved.

The key element necessary to effectuate and tying together theseteachings is the selection and use of certain polymer films as linermaterials in the production or conversion of the master rolls to beemployed in the slitting process.

Specifically, the present teachings require the use of a polymer film asthe liner material wherein the polymer film:

-   -   Is composed of a material that is compatible for use with the        matrix resin of the prepreg material and, most preferably, will        not chemically react with one another. For example, the polymer        film (a) will not accelerate or promote cure of the curable        matrix resin or, conversely, prevent or retard cure in the case        of a thermoset/thermosetting matrix resin; (b) degrade or        otherwise adversely affect the properties of the polymer in the        case of the thermoplastic matrix resin and/or (c) will not be        adversely affected by the matrix resin;    -   Manifests sufficient adhesive or peel strength when in contact        with the prepreg material to withstand the stresses of the        winding, slitting and rewinding operations without separating        from the prepreg sheet during the winding and slitting thereof        or from the slit tape, even at narrow widths, during the winding        thereof, but is readily and cleanly removed from the slit tape        without compromising the dimensions thereof and, preferably,        without leaving remnants of the film on the surface of the slit        tape;    -   Has a flexibility sufficient to accommodate the winding about a        spool or spindle without creating stresses or weakness in the        liner which may affect the dimensions and/or strength of the        liner or, more critically, the slit tape to which it is mated;        and    -   Has a sufficiently high yield strength whereby the liner will        not deform even under high stresses encountered in the slitting        and rewinding process and preferably, even under higher stresses        as may be encountered if, for example, the slit tape winders        continue to wind though prepreg is not progressing though the        slitters.

Preferably the polymer film:

-   -   has a thickness of up from about 0.1 to about 12 mils,        preferably 0.5 to about 5 mils, more preferably from about 1 to        about 2.5 mils;    -   has a 100-950% elongation whereby once yield strength is        reached, it will elastically and plastically deform and elongate        to prevent or delay a break in the liner and, coincidently the        slit tape; and/or    -   a surface energy on one side that is different from the surface        energy on the other such that the film preferentially and more        strongly bonds to the slit tape to which is it first mated        rather than the underlying slit tape upon which it is wound.    -   has a coefficient of friction of 0.1 to 0.9 such that the        polymer film spools and the slit tape/polymer liner spools will        keep stable format and shape.    -   Has a machine direction tensile strength of 500 psi to ˜40000        psi and a traverse direction tensile strength of 500 psi to        30000 psi such that the liner will not deform even under high        stresses encountered in the slitting and rewinding process    -   Has an arithmetic average surface roughness of 0.01 um to 150        um, preferably from 0.1 um to 100 um, to provide sufficient        adhesive or peel strength when in contact with the prepreg        material and to sufficient release when slit tape spools are        unwound during later manufacturing process.

The foregoing is intended to provide the basic parameters from whichthose skilled in the art will be able to identify and select appropriatepolymer films for use in the practice of the present teachings. In thisregard, it is to be appreciated that a variety of factors and conditionswill affect the selection of the polymer film including the chemistryand cure characteristics of the matrix resin; the chemistry and physicalparameters of the polymer film; the tack of the matrix resin, especiallyunder the slitting conditions; the speed and line tensions in theslitting and winding process; etc. For example, while a film of lowsurface energy may be best for use with a prepreg that has a high degreeof tack, a film of high surface energy would be preferred with a prepregmaterial with a low degree of tack, at least under the conditions atwhich the film and slit tape are mated. Similarly, polymer filmstypically have residual catalyst, stabilizers, plasticizers and the likein their composition, each of which may interact with components of thematrix resin of the prepreg. Thus, it is important to select films thatdo not have constituents or residual constituents that may impact thecure characteristics of the matrix resin. Conversely, care must also betaken to ensure that the components of the matrix resin do not adverselyaffect the physical properties and attributes of the polymer film. Forexample, it is important that the components of the matrix resin do notrender brittle, weaken, or cause crazing in the film.

As noted, and evident from the foregoing, it is not possible to defineeach of the desired, if not required, characteristics of the polymerfilm in a quantitative manner since, clearly, selection depends upon ahost of considerations and factors, not the least of which is themake-up of the prepreg materials being wound and slit. Nonetheless,despite the general description of the polymer film, it is believed thatthose skilled in the art, having the benefit of the present teachings,will readily appreciate and identify suitable polymer films for use witha given matrix resin and slitting conditions or will be readily able toascertain the same by simple trial and error.

Notwithstanding the foregoing, it is to be appreciated that suitablepolymer films include those made of polyolefins, polyamides, polyesters,vinyl polymers, polyacetates and the like: though again, not all,including not all within a given family of polymers, may be suitable forany given matrix resin. Exemplary polymer films suitable for use in thepractice of the present teachings include those made of polyethylene(PE), including low density polyethylene, high density polyethylene, andlinear low density polyethylene; polypropylene, biaxially orientedpolypropylene, polyethylene-propylene copolymer, polytetrafluroethylene,polyvinyl acetate, polyvinyl chloride, polyvinyl alcohol, ethylenevinylacetate (EVA), EVA-PE blends, polystyrene, biaxially orientedpolystyrene, polyethylene terephthalate, polyamide 6, polyamide 6,6,cellulose triacetate, just to name a few. Most preferably, the polymerfilm is a polyolefin, especially polyethylene.

Turning back to the initial focus of the present teachings, there isprovide a method for the production of slit tape from continuous prepregsheet materials wherein the method comprises passing the pre-preg sheetmaterial with liner attached through the slitter element so as toconcurrently slit the prepreg tape and liner. This contrasts withconventional pre-preg slitting processes which involve the removal ofthe backing or liner as the prepreg material is being fed to the slitterand the subsequent interleafing of a new liner material as the slit tapeis being wound. This and other distinctions between conventionalprocesses and apparatus and those according to the present teachings arebetter explained in conjunction with reference to FIGS. 1 and 2.

FIG. 1 depicts a schematic side view of a traditional slitting apparatuswhereas FIG. 2 depicts a simplified and less costly apparatus accordingto the present teachings. Each apparatus, 1 in FIGS. 1 and 2 in FIG. 2,comprises three distinct sections, a front end section (A) in which themaster roll is located, a mid-section (B) where the prepreg sheet isslit, and an end section (C) where the slit tape is wound.

The mid-section (B) is the same in both figures and comprises a slitter5 which slits the prepreg sheet 3 into the desired number of slit tapes4 of pre-determined width(s). Optionally, though preferably, and asshown in FIGS. 1 and 2, the mid-section also comprises a splicer 7 forsplicing the trailing end of one master roll to the forward end of asecond master roll. Spicing allows for the production of rolls, pancakesor spools of slit tape of specific lengths regardless of the length ofthe prepreg sheet on the master roll. Splicing also allows for theinsertion of a blank material, e.g., a liner material, so as to “prime”the apparatus for subsequent use after a given slitting operation iscompleted. Specifically, when the run of slitting is completed, themaster roll is removed. If prepreg sheet material remains on the masterroll it is cut at a point prior to the splicer. A roll of liner replacesthe master roll of prepreg sheet and the liner unwound and the forwardend thereof spliced to the tail end of the prepreg sheet. The slittingprocess is resumed and as the remaining prepreg sheet is pulled throughthe apparatus, it likewise pulls the liner. Once the slit tape is fullywound, the liner is cut at the winder and the apparatus shut down. Toreinitiate the apparatus, one merely has to cut the liner at the roll,remove the roll of liner and splice the cut end of the liner to the foreend of the prepreg sheet of a new master roll, and then resume slitting.

The first difference between the prior art slitting apparatus 1 and theapparatus according to the present teaching 2 is noted in the front endsection A. The prior art apparatus of FIG. 1 comprises a master roll ofprepreg sheet 9, a plurality of placement and alignment rollers 11 forproperly aligning the prepreg sheet 3 for advancement to the mid-sectionB. Two such rollers are shown in FIG. 1, though a single roller or morerollers could also be employed. At the second roller the backing ispeeled from the prepreg sheet and wound on a backing winding spool 12.In this manner, only the prepreg sheet passes through to the mid-sectionand the slitting operation.

In contrast, as evident from FIG. 2, the front end section of theslitting apparatus comprises a master roll 15, though in this case themaster roll has a liner of a polymer film which has replaced theoriginal backing in accordance with the teachings herein. Here, theprepreg sheet is unwound from the master roll and is advanced directlyto the mid-section and the slitting operation. Preferably, and as shownin FIG. 2, there is one or more placement and alignment rollers 17 whichhelp align the advancing prepreg with the slitter. Here, there is noneed for excess rollers nor, more importantly, a winder and windingspool for the backing material as the liner material in this embodimentremains adhered to the prepreg material throughout the process.

Other differences lie in the end section (C) which comprises a pluralityof winding stations for the slit tape, four as shown in the figures. InFIGS. 1 and 2, the winding stations of each comprise a plurality ofplacement and alignment rollers 20 and a winder 22 where the slit tapeis wound about a spool, spindle or like core element. The prior artwinding stations of FIG. 1, further comprise a feed or supply 24 ofliner tape 25 and a plurality of placement and alignment rollers 20/26for aligning the liner with the slit tape prior to their being wound atthe winder. These elements are not necessary nor present in theapparatus of FIG. 2.

Furthermore, while both apparatus employ a plurality of placement andalignment rollers in the end section, the prior art apparatus employmore as one must align both the liner and the slit tape. Moreimportantly, the prior art apparatus require rollers of higher precisionas they must properly align and overlay the liner on the slit tape asthey are mated and before they are wound on the winder. Finally, thoughnot shown, the conventional apparatus of FIG. 1 also require a pluralityof tensioning devices, controllers, sensors, and the like formaintaining a proper tension in the liner material as it is mated withthe slit tape. The failure to maintain a proper tension results in orcertainly increases the likelihood of misalignment of the liner and slittape which can lead to direct contact and adherence or melding betweensuccessive layers of the slit tape as it is wound.

All of these additional elements and operations of the conventionalapparatus and process add considerable operating costs and capitalexpense to slitting process: costs and expenses that are accentuated bythe fact that each winding station or head must have its own liner feedand associated elements. Accordingly, the apparatus of the presentteachings provides a much simpler and less costly apparatus whileproviding the same, if not a better, slit tape product in a more costeffective manner.

As noted, a key aspect to realizing the benefit of the present teachingsis the production of master rolls of prepreg materials wherein the lineris a polymer film liner that is firmly adhered to the prepreg sheetmaterial across its full width and along its full length and manifeststhe properties and characteristics as set forth above. Traditionalmaster rolls are not suitable for many reasons, as noted in thebackground section. Rather, one must either manufacture master rollsaccording to the present teaching or convert traditional master rolls tothose in accordance with the present teaching. The former requires thein-line i) removal of the backing used in the manufacture of the prepregsheet materials once the prepreg material has set sufficiently to allowsuch processing without altering the dimensions or consistency thereofand ii) the replacement thereof with a polymer film liner according tothe teachings above. The latter involves a roll to roll unwinding andwinding of the prepreg sheet with the removal of the backing and theinsertion of the polymer film liner occurring between the two rolls.

FIGS. 3A, 3B and 3C depict three of the many possible options by which aconventional apparatus for the production of continuous prepreg sheetmaterials may be altered or redesigned to make it capable of producingcontinuous prepreg sheet material for use in the practice of the presentteachings. A conventional prepreg manufacturing apparatus typicallycomprises a frame having a moving, continuous platform, typically aconveyor belt or like apparatus, upon which is fed and laid a continuoussheet of a backing material, typically paper. The platform willtypically have sidewalls so as to form a shallow trough the length ofthe platform in which the backing lay. The apparatus further comprisescomponents for supplying to and laying upon the moving backing a feed ofcontinuous fibers, in an aligned parallel relationship, and athermosetting matrix resin, typically in a molten or liquid state. Onceapplied to the backing, the resin and fibers are pressed together, oftenby one or more rollers and/or squeegee-like elements that bridge thewidth of the platform from one side wall to the other. Depending uponthe nature of the thermosetting resin, the moving platform may carry themass through one or more curing stations where the mass is subjected toconditions that partially cure or render the mass in a green state,without fully curing or cross-linking the matrix resin. Alternatively,or in addition, the matrix resin may simply set by cooling in which casethe platform may continue until sufficient cooling has been attained orpast cooling elements that enhance cooling. Once the so formedcontinuous prepreg sheet material has hardened sufficiently so as toshow minimal signs of flow or creep and to allow winding withoutaltering the thickness of the sheet, e.g., without causing the resinmatrix to flow and be squeezed out of the winding as it is being wound,the prepreg sheet, with backing attached, is wound on a master spindleor core element and stored under low temperatures for subsequent use.

FIG. 3A depicts a portion of a continuous prepreg sheet formingapparatus wherein a subapparatus 30 for removing the backing andreplacing it with a polymer film liner is incorporated into the movingplatform at a point along the length of the moving platform where thematrix resin is sufficiently solidified so as to maintain its shape andintegrity while removing the backing and in the absence of the backing.Specifically, as seen in FIG. 3A, the tail end of one moving platform 32is adjacent, but spaced from, the fore end of a second, successivemoving platform 34. In this figure, the moving platform comprises aplurality of conveyor belts 36 continuously rotating about theirrespective axels 38. The gap between the ends of the two conveyor beltsserves as the operative region where the backing 40 on the prepreg sheetmaterial 42 is removed or peeled from the prepreg at roller element 43and wound upon a backing take-up winder 44. Concurrently, a continuouspolymer film liner 46 is unwound from a supply spool 45 and aligned withand mated with the prepreg sheet material 42 by a plurality ofpositioning and alignment rollers 47. One or more of these rollers mayalso be positioned, configured or constructed to press the liner to theprepreg sheet material as it passes over or between the rollers. In thisembodiment, the newly lined prepreg sheet material continues on for fullsetting to its green state or winding state for subsequent operation,which could be winding or slitting.

FIG. 3B depicts an embodiment wherein a subapparatus 50 for removing thebacking 51 and replacing it with a polymer film liner 53 is incorporatedinto the moving platform at the tail end of the moving platform 52,intermediate the moving platform and the master roll winder 54 forwinding the prepreg sheet 56. It is also to be appreciated that whileFIG. 3B shows the moving platform 52 in close proximity to the masterroll winder 54, such is not necessary. The winder may be placed somedistance from the moving platform provided that there are appropriatepositioning and alignment rollers in place to support the prepreg sheetbetween the moving platform and the subapparatus, or if the latter iscloser to the moving platform, between the subapparatus and the winder.

In FIG. 3B the moving platform comprises a conveyor belt 58 continuouslyrotating about its respective axels 60. As the prepreg sheet travelspast the end of the conveyor belt it engages a roller element 62 whichfacilitates the removal and peeling of the backing 51 from the prepregsheet 56, which backing is then taken up by backing take-up winder 64.One or more positioning and alignment rollers 55 may also be present toensure continued alignment of the prepreg sheet as it continues to moveforward through the subapparatus. Concurrently, a continuous polymerfilm liner 53 is unwound from a supply spool 65 and aligned with andmated with the prepreg sheet material 56 by a plurality of positioningand alignment rollers 66. One or more of these rollers 68 may also bepositioned, configured or constructed to press the liner to the prepregsheet material as it passes over or between the rollers. Finally, theprepreg sheet with the polymer film liner is then wound about a spool,spindle or core element on master roll winder 54. Once completed, themaster roll is then removed and placed in cold storage to cool.

FIG. 3C depicts an embodiment wherein a subapparatus 70 for removing thebacking 71 and replacing it with a polymer film liner 74 is incorporatedinto the apparatus associated with the continuous manufacture andslitting of prepreg tape. In this particular figure, the subapparatus ispositioned after the end of the moving platform, at a point where theprepreg sheet and liner are self-supporting and do not require thepresence to the platform. Instead, a plurality of positioning andalignment rollers 76 position and carry the prepreg sheet to and throughthe subapparatus 70. Still, it is to be appreciated that thesubapparatus could be incorporated at the tail end of the movingplatform, as indicated in FIG. 3B.

As the prepreg sheet advances into the subapparatus, it engagespositioning and alignment roller 78 which also facilitates the removaland peeling of the backing 71 from the prepreg sheet 72, which backingis then taken up by backing take-up winder 80. Concurrently, acontinuous polymer film liner 74 is unwound from a supply spool 82 andaligned with and mated with the prepreg sheet material 72 by a pluralityof positioning and alignment rollers 84. One or more of these rollers 88may also be positioned, configured or constructed to press the liner tothe prepreg sheet material as it passes over or between the rollers.From there, the prepreg sheet advanced directly into the slitter 90 forslitting and on to the appropriate winding apparatus for winding the soformed slit tape. In this embodiment, it is preferred that the matedpolymer film liner and prepreg sheet material are pressed together,especially by press rollers to ensure sufficient adherence or tackbetween the two. This is not as critical a factor in the embodimentwhere the prepreg sheet material is wound in a master roll as thewinding and weight of the master roll itself ensures a proper bond.

It is also to be appreciated that the subapparatus of FIG. 3C could alsobe incorporated into a slitting apparatus between the master roll andthe slitter. In this manner, the removal of the backing and insertion ofthe polymer film liner occurs in-line in the slitting apparatus andmethod.

In accordance with another embodiment of the present teachings, there isprovided a process and apparatus for converting conventional masterrolls to master rolls suitable for use the practice of theaforementioned slitting process wherein the liner and prepreg materialsare slit concurrently. Although the foregoing embodiments provideapparatus for the direct production of such suitable master rolls aswell as subapparatus that may be retrofitted into existing prepreg sheetmanufacturing and/or slitting apparatus, such entails added capitalexpense and may not be possible given processing and spacinglimitations, at least not without substantial realignment andreconfiguration of equipment and apparatus.

Accordingly, as shown in FIG. 4, there is provided an apparatus 100 forconverting conventional master rolls of prepreg sheet to those having apolymer film liner as required for used in the practice of the presentlytaught slitting process. This apparatus comprises four distinctstations. The first is that station wherein a master roll 102 of prepregsheet 104 with the backing 103 intact is unwound and fed into the secondstation where the backing is removed and wound about backing take-upwinder 106. The prepreg sheet 104 continues to the third station where apolymer film liner 108 and the prepreg sheet are aligned and mated. InFIG. 4, this point is shown by roller 110. The polymer film liner issupplied from stock roll of polymer film 112. The mated polymer filmliner and prepreg sheet then pass over and through one or moreadditional positioning and alignment rollers 114, which may or may notapply pressure to the mated liner and prepreg sheet material to enhancebonding. The mated liner and prepreg sheet is then advanced to a windingstation where it is wound into a master roll 116. The so formed masterroll is then ready for use in the practice of the herein taught slittingprocess.

In each of the processes for the production of the master rollsdescribed above, it is to be appreciated that the width of the polymerliner material may be the same as, but, is preferably slightly widerthan the width of the prepreg sheet to which it is being mated. Thoughgrooved rollers, especially double grooved rollers, will assist inensuring proper alignment of the liner to prepreg sheet, the additionalwidth of the polymer film adds further insurance that the matrix resinof one layer in the winding will not mate with or bond with the matrixof the underlying or overlaying layer of the winding. Furthermore, sincethe edges of the master rolls upon slitting are typically discarded, anyexcess liner is likewise discarded and the slit tape produced form thesemaster rolls will have clean edges with the tape and liner directlyoverlaying one another.

The improved master rolls, prepreg manufacturing and slitting processesand apparatus of the present teachings have many additional benefits andattributes over conventional processes and apparatus beyond those of thelower capital costs and simpler apparatus and processes as describedabove. Indeed, improvements have been realized in both processing andproduct using various polymer films, especially polyethylene, mostespecially high density polyethylene, on various prepreg sheetmaterials. Specifically, slitting the prepreg sheet with the polymerfilm liner attached has led to an improvement in slit width variance,reducing slit width variation by up to 40% or more. It is thought thatthe polyliner adds structural integrity to the prepreg sheet as itpasses through the slitter counteracting the still “fluid” nature of thematrix resin. Additionally, the practice of the present teachings hasled to reduced cycle times due to less buildup of resin in the slitter,especially on the knives or blades. Such improvements approach, if notexceed, 25% with epoxy-based, carbon fiber prepregs. Additionally,improvements in cycle time performance of 100% and more have been seenin the case of bismaleimide (BMI) and polyimide based prepregs:materials that have heretofore been very difficult to slit. In thisrespect, it is thought that the polymer film liner cleans the knives orblades or functioned as a barrier preventing what build up does occurfrom contacting the slit tape as it passes by. Depending upon themake-up of the film, it may also include additives which coat the bladesor knives which prevent the build-up of resin. Production efficiency andthroughput is further enhanced, upwards of 33% or more, by the reductionin liner misalignment and, consequently, a reduction in line stoppage toaddress the misalignment.

In addition to process efficiency improvements, the product is lesscostly due to the significant reduction in liner costs. Conventionalslitting operations require one to manufacture of slit liners to besomewhat sized to the slit tape to be produced. Thus, one incurs theexpense of slitting the liner whereas the present process allows for theuse of stock master rolls of liner. Additionally, as previously noted,the conventional process requires the use of liner strips that are widerthan the slit tape: a happenstance that consumes considerably largeramounts of liner material. Furthermore, the absence of excess liner oneach slit tape, particularly given the weight and size limitations onthe rolls to be supplied to the end-users, enables for the production ofrolls of slit tape having more slit tape, hence the need for fewerchange overs of the spools or spindles in the winding process as well asby the end-user. This, in turn, leads to further increases andenhancement in the overall productivity of the slitting process as wellas the manufacturing process using the slit tape.

Although the method and apparatus of the present specification have beendescribed with respect to specific embodiments and figures, it should beappreciated that the present teachings are not limited thereto and otherembodiments utilizing the concepts expressed herein are intended andcontemplated without departing from the scope of the present teaching.Thus true scope of the present teachings is defined by the claimedelements and any and all modifications, variations, or equivalents thatfall within the spirit and scope of the underlying principles set forthherein.

We claim:
 1. A method of preparing a continuous sheet of prepregmaterial suitable for use in a slitting process for the production ofslit tape which slitting process does not require the removal of a lineror backing prior to slitting nor the insertion of a liner prior towinding the slit tape so formed, the method comprising: a) unwinding amaster roll of a continuous sheet of prepreg material having a paper orpolymer film backing attached, b) removing the backing from the prepregmaterial, c) aligning and mating a polymer film liner with the prepregmaterial, and d) rewinding the mated prepreg material and polymer filmliner to form a new master roll; wherein the liner is a polymer filmwhich is 1) able to be slit by the slitter without tearing, without theformation of fibrils, and without separating from the prepreg material;2) resists elongation and/or the creation of stress fractures in thefilm under the stress of winding, and 3) manifests a sufficient adhesiveor peel strength with the prepreg material so as avoid separating fromthe prepreg material under the stresses of the unwinding, slitting andwinding processes.
 2. The method of claim 1 wherein the liner iscomposed of a material that is compatible with the matrix resin of theprepreg material.
 3. The method of claim 1 wherein the liner is composedof a material that has a thickness of 0.1 to about 12 mils, a lengthwisetensile strength of 500 psi to 40,000 psi, and an arithmetic averagesurface roughness of 0.01 to 200 um.
 4. The method of claim 1 whereinthe polymer film liner is composed of a polyolefin, a polyamide, apolyester, a vinyl polymer, or a polyacetate.
 5. The method of claim 1wherein the polymer film liner is polyethylene.
 6. A master roll of acontinuous sheet of prepreg material, said master roll having beenformed by a method comprising: a) unwinding a master roll of acontinuous sheet of prepreg material having a paper or polymer filmbacking attached, b) removing the backing from the prepreg material, c)aligning and mating a polymer film liner with the prepreg material, andd) rewinding the mated prepreg material and polymer film liner to form anew master roll; wherein the liner is a polymer film which is 1) able tobe slit by the slitter without tearing, without the formation offibrils, and without separating from the prepreg material; 2) resistselongation and/or the creation of stress fractures in the film under thestress of winding, and 3) manifests a sufficient adhesive or peelstrength with the prepreg material so as avoid separating from theprepreg material under the stresses of the unwinding, slitting andwinding processes.
 7. The master roll of claim 6 wherein the liner iscomposed of a material that is compatible with the matrix resin of theprepreg material.
 8. The master roll of claim 6 wherein the liner iscomposed of a material that has a thickness of 0.1 to about 12 mils, alengthwise tensile strength of 500 psi to 40,000 psi, and an arithmeticaverage surface roughness of 0.01 to 200 um.
 9. The master roll of claim6 wherein the polymer film liner is composed of a polyolefin, apolyamide, a polyester, a vinyl polymer, or a polyacetate.
 10. Themaster roll of claim 6 wherein the polymer film liner is polyethylene.11. An apparatus for the conversion of master rolls of continuous sheetsof prepreg materials having a paper or polymer film backing to a masterroll of a prepreg material having a liner whereby the prepreg materialmay be slit with liner attached, said apparatus comprising a master rollstation for holding and unwinding the original master roll, a separatorstation wherein the backing of the original master roll is removed fromthe prepreg sheet material, a lining station wherein the prepregmaterial is aligned with an mated to a polymer film liner, and a windingstation wherein the prepreg and liner are wound into a new master roll.12. The apparatus of claim 11 wherein the master roll station comprisesan axel, which may be motorized, upon which the master roll of prepregmaterial is to be mounted; the separator station comprises a motorizedaxel upon which a spindle is to be mounted for taking up and winding thebacking as it is removed from the prepreg sheet material; the liningstation comprises an axel, which may be motorized, upon which a roll ofliner material is to be placed, and alignment mean for aligning andmating the liner material with the prepreg material; and the windingstation comprises a motorized axel upon which a spindle is to be mountedabout which the prepreg and liner combination is to be wound.
 13. Theapparatus of claim 12 further comprising a roll of a polymer film placedon the axel of the lining station wherein the polymer film is 1) able tobe slit by the slitter without tearing, without the formation offibrils, and without separating from the prepreg material; 2) resistselongation and/or the creation of stress fractures in the film under thestress of winding, and 3) manifests a sufficient adhesive or peelstrength with the prepreg material to be slit so as avoid separatingfrom the prepreg material under the stresses of the unwinding, slittingand winding processes.
 14. The apparatus of claim 13 wherein the lineris composed of a material that has a thickness of 0.1 to about 12 mils,a lengthwise tensile strength of 500 psi to 40,000 psi, and anarithmetic average surface roughness of 0.01 to 200 um.
 15. Theapparatus of claim 13 wherein the polymer film liner is composed of apolyolefin, a polyamide, a polyester, a vinyl polymer, or a polyacetate.16. The apparatus of claim 13 wherein the polymer film liner ispolyethylene.
 17. An improved process for the production of master rollsof continuous sheets of prepreg material adapted wherein the improvementcomprises using a polymer film liner material as the backing in thepreparation of the prepreg sheet wherein the liner is 1) able to be slitby the slitter without tearing, without the formation of fibrils, andwithout separating from the prepreg material; 2) resists elongationand/or the creation of stress fractures in the film under the stress ofwinding, and c) manifests a sufficient adhesive or peel strength withthe prepreg material so as avoid separating from the prepreg materialunder the stresses of the unwinding, slitting and winding processes. 18.The improved process of claim 17 wherein the liner is composed of amaterial that is compatible with the matrix resin of the prepregmaterial.
 19. The improved process of claim 17 wherein the liner iscomposed of a material that has a thickness of 0.1 to about 12 mils, alengthwise tensile strength of 500 psi to 40,000 psi, and an arithmeticaverage surface roughness of 0.01 to 200 um.
 20. The improved process ofclaim 17 wherein the polymer film liner is composed of a polyolefin, apolyamide, a polyester, a vinyl polymer, or a polyacetate.